The Reflex Auto will automatically turn on whenever both darkness and motion are detected by the motion and light optic sensors, providing the rider safety both while the light is turned on and while functioning solely as a reflector. 5 LEDs Greater than 180 degree visibility Automatically turns on / off by light and motion sensors Emits light for 50 seconds after the bike stops Built-in reflectors that meets highest government standards (USA, Great Britain, Europe and Japan) OptiCube™ lens technology AAA alkaline battery x 2 5 modes Mode memory function SP-5 bracket (ø21.5-31.8mm) and Rear rack bracket